1. Field of the Invention
The present invention relates to temperature conditioning systems and, more particularly, to a temperature conditioning system for select heating and liquid constituent control of liquids and/or solids through the control of enthalpy, partial pressures and dew point within a heating medium comprising a mixture of condensible and non-condensible gases.
2. History of the Prior Art
The prior art is replete with heating systems for both solids and liquids. Many of these systems incorporate direct contact heat exchange wherein the temperature of the heating medium is the single-most critical operational parameter. The contact is generally made between the substance to be heated and the products of combustion from a furnace or the like.
U.S. Pat. No. 4,275,708 to Wood teaches a method and apparatus for direct contact water heating utilizing the direct heat of combustion for developing hot water. A vessel is set forth therein containing a plurality of heat absorbing bodies which act in combination as a heat exchanger and also as an oxygen stripping chamber. The lower compartment within the vessel comprises a combustion chamber and reservoir for storage of the hot water heated in the furnace.
While the aforesaid prior art systems are effective in overcoming many of the disadvantages of prior art direct contact combustion heating systems, numerous inherent problems remain. Serious concerns in direct contact combustion furnace heating systems include high contact temperature, corrosion, heat distribution, oxidation, and incompatibility with certain substances to be heated. The results of combustion of a conventional furnace include (a) intense heat of both radiant and convective varieties, (b) non-combustibles, and (c) the products of combustion including carbon dioxide and water. When the substance to be heated is sensitive to either intense heat and/or the products of combustion in the presence of intense heat, the aforesaid furnace configurations are not useful. In such circumstances heating systems incorporating boiler networks have been implemented. In these systems, the heat of combustion is first transferred to a vessel containing water which is converted into steam and used as the heating medium.
The prior art of boiler heating systems extends into technological antiquity. Steam from boiler systems has been utilized for comfort heating as well as commercial heat application for many decades. Other applications of conventional steam boilers include the treatment of solids such as tobacco leaves, grain, flour and animal feed. For example pelletized animal feed is often treated with steam to improve the pelletizing operation and digestibility of the feed by the animal. The steam which heats the feed is generally injected into the feed prior to pelletizing to condition it. The feed coming to the pelletizer often has between eleven and twelve percent moisture and is at ambient temperature. The steam system conditioning equipment raises the temperature of the feed as close as possible to approximately 200.degree. to improve the digestibility by the animal. It is necessary, however, to assure that none of the feed gets so hot as to scorch the feed or break down the vitamin additives Unfortunately, with live steam, the maximum temperature rise that can be produced by a boiler system without adding so much water that the pelletizing is no longer feasible is approximately 120.degree. F. Thus, with an adequate boiler, 200.degree. F. feed can be obtained only when the incoming feed is at or above 80.degree. F. At other times, and particularly in the winter, feed temperature of about 160.degree. F. to 180.degree. F. is the maximum attainable.
Other prior art grain treatment systems have addressed the need for moisture control with apparatus which introduces steam and air in combination. For example, U.S. Pat. No. 1,185,622 to Boss teaches a 1916 process of conditioning food forming substances. The Boss patent sets forth the moisture treatment of grain or the like in such a manner that it is hydroscopically conditioned by either adding or taking moisture from such particulate matter. These systems are useful in preparing the grain to a condition where it is uniformly hydrous in its character. Such product is more thoroughly digested in given quantities, in shorter time and with greater nutritive and body building effect. It has thus been a goal in the prior art grain condition technology to provide a treating "fluid" capable of delivering or withdrawing moisture or other substance to or from the material to be acted upon for swelling or shrinking or wetting or drying the material as needed. To affect this end result, air and steam have been utilized in various heating and flowing configurations such as that initially shown in the Boss patent. This prior art does not envision heating the grain to a controlled higher temperature so as to cook it for better digestibility.
More advanced prior art grain treatment technology has generally included refinements on the age old principle of steam moisturizing. For example, U.S. Pat. No. 1,574,210 to Spaulding teaches a method and apparatus for steaming grain and the like. The Spaulding system utilizes gravity descent and angularly disposed baffles for deflecting the grain. Steam supply ports are provided for the steaming operation of the grain during its descent. A prior U.S. patent issued to Henson under U.S. Pat. No. 1,174,721 sets forth an improved method of supplying moisture to grain and the like by utilizing the flow of steam and air heated by said steam prior to entry into a treatment chamber. Moisture is added to the particulate matter such as grain by introducing steam with the air prior to entry into the treatment chamber. The Henson patent further teaches the use of a hygrometer to determine the moisture content of the air. Grain which is fed into the interior of the mixing treatment chamber comes in contact with the vapor which tends to condense thereupon. In this manner, the amount of moisture deposited in the substance passing through the treatment chamber may be calculated from the data given. Such a system will also work with raw steam being used instead of the mixture of steam and air.
These prior art grain treatment systems have been shown to be effective in removing or adding moisture to grain. Unfortunately, the degree of moisture contributed to the particulate matter is generally hard to control and/or define in any empirical manner short of raw data measurements such as that discussed above. Moreover, these prior art systems do not envision control of heat added to the grain.
Some conventional technology has addressed the issue of control of various aspects of steam itself including both the adding of moisture to and removal of moisture from particulate matter. For example, U.S. Pat. No. 4,024,288 issued to Witte illustrates a method of treating particulate matter for conditioning oil containing vegetable raw materials. In the Witte patent, air and steam are again utilized for the treatment of the raw material. The utilization of super-heated steam coming from a heat exchanger which is then mixed with air is set forth and shown in the Witte reference and discloses an effective means for immersing the raw material into a steam and hot air bath. Material leaving the bath is then dried by air issuing from a hot air heat exchanger. While effective in heating by means of steam, Witte maintains little control over the temperture to which the raw material is heated and requires two separate fluid stream to attain the desired temperature and moisture levels.
U.S. Pat. No. 4,249,909 issued to Comolli sets forth a staged process for drying wet carbonaceous material. The stage drying procedure permits wicking up of hydrocarbons contained in coal to seal the surface of dried coal products sufficient to prevent appreciable reabsorption of moisture and consequent heating and spontaneous ignition. The Comolli procedure was developed for this particular application and in so doing manifested the advances made in the state of the art in steam treatment systems. These advances may be seen in part in the efforts to define and control various parameters of steam such as partial pressures. The pressures exerted by each constituent alone in the volume of a mixture at the temperature of the mixture are called partial pressures. The partial pressure is directly related to the mole fraction of a constituent present in a mixture and the total pressure thereof.
Control of partial pressure in a steam heating medium affords numerous benefits. For example, the heat treatment of coal as set forth in the Comolli patent illustrates the feasibility of controlling partial pressures in steam for purposes of controlling the rate of "drying" and prevention of the "pop corn" effect. Removal of surface moisture from the coal is therein accomplished rapidly with circulating moist air at atmospheric pressure and about 220.degree. F. dry bulb temperature and 130.degree. F., wet bulb temperature. In the second stage, steam is supplied to provide a more humid environment with the wet bulb temperature of the circulating air at about 160.degree. F. so as to provide therein a lower water partial pressure differential relative to that of the coal. This more humid condition results in slower removal of additional moisture from the coal particles so that not only is particle rupture prevented, but also low volatility hydrocarbons and tars contained in the coal are wicked to the surface where they serve to substantially seal the pores.
It may thus be seen that the treatment of particulate matter with steam has evolved through the years through the utilization of steam as a drying medium. The advantages of steam as a moisturizing and heating medium for food stuffs such as grain and flour may likewise be useful if the end product can be selectively controlled. Conventional treatment processes for cellular matter such as grain generally use raw steam as a sole element of a heating medium or in combination with air or similar non-condensible gases for the moisturizing process. Such processes are typically incapable of effectively treating the cellular particulate matter in the precise manner necessary for maximum utilization. For example specific moisture levels, heat absorption and final grain temperatures must be obtained for reliable and effective conditioning. Reasons for the inability of conventional apparatus to meet such demands of the market are due to their inability to simultaneously control moisture content, heat absorption and final product temperature.
It would be an advantage, therefore, to provide a system for select temperature and moisture conditioning of either liquids or solids by controlling the enthalpy, partial pressures and dew point of the heating medium. The system of the present invention affords such an operation by utilizing a steam vapor generator, or the like in conjunction with a flow system for the heating of both liquid and/or solids passed therein. The rate of heat supplied, may therein be controlled by the rate of fuel burning while the moisture content and the maximum temperature generated in the product can be controlled through the partial pressure of the condensible vapor and dew point. The partial pressure and dew point are, in turn, determined by the fluid flow rates in the vapor generator and/or the introduction of extra amounts of non-condensible gas and the total pressure at which the system operates.